The invention relates to a steering apparatus of rack and pinion type.
A typical steering apparatus of rack and pinion type is illustrated in FIG. 1 wherein a steering body 1 includes a bearing which rotatably supports a pinion 2, which is mechanically interlocked with a steering wheel, not shown, and which meshes with a rack 3 which reciprocates axially as the pinion rotates. The apparatus also includes a support member 4 which is disposed in abutting relationship with the backside of the rack 3 to support it in a slidable manner. The support member is biased by a spring 5 to urge the rack 3 against the pinion 2. In a conventional arrangement as described, there is no change in the condition of contact between the rack 3 and the support member 4 during a stroking of the rack which occurs in response to the rotation of the pinion 2 as the steering wheel is operated. In other words, points of contact P.sub.1 and P.sub.2 between the rack 3 and the support member 4 remain at identical positions in a plane perpendicular to the axis of the rack 3, without experiencing any movement. Consequently, a sliding resistance between the rack 3 and the support member 4 remains constant and does not change over the full stroke of the rack 3.
Referring to FIG. 2 for considering a sliding resistance between the rack 3 and the support member 4 it will be seen that when the rack 3 and the support member 4 contact each other at two points, the reaction force of the spring F will be divided into vertical components of F/2 at each of the points of contact P.sub.1 and P.sub.2. Representing the angle formed between a line which is orthogonal to the component F/2 and the tangent to each of the points of contact P.sub.1 and P.sub.2 by .theta., the drag f of the support member 4 which results from the reaction force F of the spring at these points will be given as follows: EQU f=F/2/ cos .theta.
The sliding resistance R between the rack 3 and the support member 4 is given by the following equation: EQU R=f.mu.
where .mu. represents a coefficient of friction.
When the sliding resistance has a constant magnitude as in conventional arrangements, the reaction force to the steering wheel will exhibit a linear response when viewed as a steering apparatus singly. It is generally recognized that an increase or a decrease in the magnitude of the reaction force applied to the steering wheel has an effective contribution to a recognition of the steering effort by a driver when considering the steering sensation which a driver experiences in a typical vehicle. However, when the sliding resistance has a constant magnitude, it is difficult to produce an optimum steering sensation by creating a delicate change in the reaction force applied to the steering wheel.